The present invention relates generally to electric meters and, more particularly, to an electric meter that has the capability of detecting an attempt to tamper with the meter through the surreptitious use of a magnetic field.
Electric utilities have been using electric meters for many years to measure the magnitude of electrical energy consumption of its customers. In more recent years, electric utilities have begun to utilize electric meters that have the capability of communicating with a central communication station. One particular means for providing this communication capability is to utilize the power line system of the electric utility. A central transmitting and receiving station is generally provided that has the capability of sending messages to a multiplicity of remote meters that are located at consumers' residences and receiving messages transmitted therefrom.
Whether conventional electric meters or meters with transceivers are used, electric utilities face the potential problem caused by tampering with the meters. Tampering represents a significant and costly problem for electric utilities whether the tampering is caused by a consumer attemping to benefit economically from damage
Many types of tampering procedures are known to those skilled in the art of electrical metering. One particular method of tampering that is difficult for an electric utility to detect is the use of a strong magnetic field to effect the magnetism of the permanent magnets used in conjunction with a rotatable disc within the meter's structure. One way of performing this tampering procedure is to form a multi-turn coil of heavy gage wire with the ends of the wire extending from the coil. The coil could comprise approximately eight to ten turns of wire and the wire could be approximately number 12 awg. The coil of wire is then disposed around the meter and the ends of the conductor are connected in electrical communication with a 240 volt AC power source. This causes an extremely high current to flow through the conductor, reaching levels of several thousand amperes. The current flowing through the coil of wire causes a very strong magnetic field and, since the coil of wire is disposed around the meter, this magnetic field is imposed on the components of the meter. The affect of this magnetic field can permanently change the level of magnetization of the permanent magnets used in the meter.
When this type of tampering is used, the changed level of magnetization of the meter's permanent magnets causes the meter to incorrectly register a magnitude of energy consumption that is higher or lower than the amount of energy actually used. The tamperer then waits some number of billing periods following the tampering effort and registers a complaint with the electric utility that the meter is faulty. When the electric utility determines that, in fact, the meter is malfunctioning due to the changed magnetization of its permanent magnets, the tamperer can claim that the metering error existed for many months previous to its discovery. Of course, the tamperer then would insist on a retroactive reduction in previous electric bills which were, in fact, correct in their amounts.
This type of tampering procedure not only costs the electric utility money in lost billing income, but also severely damages the electric meter and necessitates its replacement. Furthermore, if this tampering procedure is performed carefully, it is very difficult for the electric utility to determine the actual cause of the demagnetization.
In the particular case where this type of tampering technique is applied to an electric meter that is equipped with a transceiver and a microprocessor, it is possible to provide a means for detecting this type of tampering techniques. The present invention provides a means for detecting the use of a magnetic field for the purpose of causing a deleterious change in the characteristics of an electric meter.
In electric meters that have the capability of transmitting and receiving messages on a power line communication system, the meter is sometimes also equipped with a magnetically actuated switch for the purposes of identifying a particular type of received transmission. One type of device used in association with a power line communication system is a field configuration terminal. The field configuration terminal, or FCT, is used by an operator to communicate with an electric meter for purposes of interrogating it or altering its memory. For example, if an electric meter is suspected of operating improperly, an operator can use a field configuration terminal for the purposes of examining the memory contents of the microprocessor within the meter. Also, the field configuration terminal can be used to request information, such as kilowatt hours or alarm status.
U.S. Pat. No. 4,467,314, which issued on Aug. 21, 1984, to Weikel et al. discloses a field configuration terminal which can be used as a combination field configuration and test terminal. U.S. Pat. No. 4,467,314 is hereby incorporated by reference.
In order for an electric meter to be used in conjunction with a field configuration terminal, the electric meter must be provided with the capability of receiving messages from a power line communication system. U.S. Pat. No. 4,382,248, which issued on May 3, 1983, to Pai, discloses a device for receiving communication signals carried by the phase conductors of a multi-phase power distribution network communication system. Although this particular device includes a circuit for independently receiving each of the communication signals carried by the phase conductors, other receiving circuits are known to those skilled in the art which can be coupled to a single phase of a power line distribution system. U.S. Pat. No. 4,382,248 is hereby incorporated by reference.
In order for an electric meter to be able to communicate with a field configuration terminal by transmitting messages to it, it must have the capability of inserting carrier frequency signal information onto the power line. U.S. Pat. No. 4,323,882, which issued on Apr. 6, 1982, to Gajjar, discloses an apparatus for inserting carrier frequency signal information onto distribution primary windings. This device and many other devices known to those skilled in the art can be used to transmit amplified signals onto a power line distribution system. U.S. Pat. No. 4,323,882 is hereby incorporated by reference.
U.S. Pat. No. 3,942,170, which issued on Mar. 2, 1976, to Whyte, discloses a distribution power line carrier communication system for providing distribution automation functions. U.S. Pat. No. 3,967,264, which issued on June 29, 1976, to Whyte et al., discloses a distribution network power line communication system which is divided into addressable communication zones defined by repeaters located at the distribution transformers of the distribution network. Both of these patents are related to power line communication systems that are suitable for use with electric meters and field configuration terminals. U.S. Pat. Nos. 3,942,170 and 3,967,264 are hereby incorporated by reference.
In a typical power line communication system, messages are coded and modulated prior to their transmission to a remote device. Although many types of modulation techniques are known to those skilled in the art, one particular technique has been widely used in power line communication systems. This technique uses a phase shift keyed modulation in which a carrier signal is modulated with a base band data message. The carrier signal is a square wave signal with a constant frequency such as, for example, 12.5 kilohertz. It should be understood, however, that many different carrier frequencies can be used. A message is first coded into a baseband data format and this baseband data message is then used to modulate the carrier frequency prior to amplification and injection onto the power line system.
A power line communication device, such as an electric meter, must also have the capability of demodulating incoming messages. U.S. Pat. No. 4,311,964, which issued on Jan. 19, 1982, to Boykin, discloses a coherent phase shift keyed (PSK) demodulator for power line communication systems that includes means for sequentially processing plus and minus polarity samples of plural carrier segments occurring within each carrier data symbol. U.S. Pat. No. 4,379,284, which issued on Apr. 5, 1983, to Boykin, discloses an improved coherent phase shift keyed demodulator for power line communication systems. U.S. Pat. Nos. 4,311,964 and 4,379,284 are hereby incorporated by reference.
When an electric utility wishes to examine the operation of one of its electric meters that is connected in signal communication with a power line communication system or alter the operation of such a meter, it can utilize a portable field configuration terminal that can be transported into the field by an operator. The design and operation of a typical field configuration terminal is described in great detail in U.S. Pat. No. 4,467,314 which issued on Aug. 21, 1984, to Weikel et al. When an electric meter is intended to be used in cooperation with a field configuration terminal, it is beneficial to utilize some additional means to verify commands received from the field configuration terminal. This is usually done since the field configuration terminal has the capability of causing significant changes to the electric meter and its associated microprocessor. One known means of verifying the authorized use of a field configuration terminal is to employ a magnetically actuated switch connected in signal communication with its microprocessor within the structure of the electric meter. When an operator performs an authorized field configuration terminal operation on an electric meter, a magnetic is first placed at a location proximate the magnetically actuated switch and then the field configuration terminal is used to send commands to the electric meter's microprocessor. Normally, if the magnetically actuated switch is not properly actuated by a magnet in this manner, the commands from the field configuration terminal are ignored to avoid drastic changes to the microprocessor's data that could be caused by an errant command intended for another purpose but incorrectly interpreted as a field configuration terminal command. The magnetically actuated switch also provides a means for preventing one load management terminal from responding to a field configuration terminal's message that is intended for another load management terminal. Since the messages, between field configuration terminals and load management terminals, are injected onto the power line system, other nearby load management terminals will receive and demodulate the messages. Although other means are provided for load management terminals to verify the intended recipient of each message, the magnetically actuated switch provides additional security for this purpose.
In situations where the electric meter is provided with a magnetically operated switch, such as a read switch, a tamper detection scheme can be employed that can sense, record and report the existence of a magnetic field proximate the electric meter. Of course, when a field configuration terminal is used in conjunction with an electric meter, the magnetic field is intentionally applied by the use of a permanent magnetic and this presence of a magnetic field is authorized and legitimate. However, if a coil of wire is used to create a strong magnetic field proximate the electric meter for the purpose of tampering with its operation, the magnetically operated switch can be utilized to detect this tampering procedure. The ability to detect this type of tampering effort would be significantly beneficial to an electric utility.
The present invention provides a means for detecting the presence of a magnetic field proximate an electric meter. Furthermore, it provides a means for recording this occurrence and reporting it to either a remote station on the power line communication system or an operator using a field configuration terminal.
An electric meter made in accordance with the present invention comprises a magnetically sensitive switch and a means for sensing the state of the switch. The sensing means can be microprocessor connected in signal communication with the magnetically sensitive switch. The present invention also incorporates a means for recording the occurrence of the activated status of the switch, which can be accomplished by the use of the microprocessor, and a means for determining the legitimacy of the activated status of the switch. For example, if the present invention records the occurrence of a magnetically sensitive switch activation, but does not experience any legitimate field configuration terminal commands, this combination of indicators, or flags, is indicative of the fact that a tampering procedure utilizing a magnetic field has occurred.
The present invention also incorporates a means for communicating these status flags to remote devices. The status of the occurrence of a magnetically operated switch activation is stored in the non-volatile memory of a microprocessor system and reported, as one or more bits in a status word, during subsequent transmissions to the central station. In a preferred embodiment of the present invention, the magnetically sensitive switch is a reed switch.
In an electric meter made in accordance with the present invention, a program within its microprocessor is caused to be executed many time a second. For example, if a 60 hertz pulse is used as the activation mechanism, the program within the microprocessor would execute 60 times each second. Upon each execution of the program, the status of the magnetically activated switch is interrogated and the result is stored if an activation is sensed. Also, if a legitimate command from a field configuration terminal is received, this occurrence is also recorded in the memory of the microprocessor. Therefore, these two indicator flags can be used to determine whether or not a magnetic field was experienced by the electric meter or a field configuration terminal command was received. If the magnetic field occurred without the concurrent use of a field configuration terminal, a tampering effort is indicated.
The present invention also incorporates means for transmitting data messages to remote devices and for receiving data messages therefrom. Therefore, the present invention provides an electric meter with the capability of indicating, to a remote central station, the occurrence of a magnetic tampering effort.